In a gasoline engine, the vehicle is set in driving operation and/or the driving operation is maintained as the result of combustion of the supplied fuel-air mixture. The combustion of the fuel-air mixture is initiated by the ignition spark of a spark plug. As the flame front propagates in the combustion chamber, the high pressures and temperatures result in auto-ignitions in the end-gas zone. The combustion, which then proceeds suddenly, causes a great pressure rise in the combustion chamber of the gasoline engine which generates a pressure wave that propagates and strikes the walls adjoining the combustion chamber, where the high-frequency oscillations are converted into structure-borne noise. These oscillations are detected by knock sensors (structure-borne noise sensors) and taken into account in controlling the gasoline engine by knock control in order to prevent engine damage. The gasoline engine is always operated at the knock limit in an efficiency-optimized manner, thus avoiding damage to the gasoline engine as a result of the knocking.
However, in addition to the described knocking combustions, auto-ignitions occur as the result of hot spots in the combustion chamber, oil droplets, or hot residual gas zones in the fuel-air mixture. Such auto-ignitions may appear as pre-ignitions before the ignition spark occurs, and as post-ignitions after the ignition spark occurs. The auto-ignitions are characterized by combustion pressures having high pressure amplitudes, which may very quickly result in engine damage.
European Patent No. EP 1 715 179 A2 describes determining premature combustions with the aid of the knock sensor. However, since such auto-ignitions involve a knocking combustion only to a limited degree due to high-frequency pressure components, it is not possible to detect auto-ignitions, which have predominantly low-frequency pressure patterns which do not affect the structure-borne noise of the combustion chamber walls, using knock sensors.